Electric switches



Oct. 6, 1959 R. A. FIRMAN 2,907,854

I ELECTRIC SWITCHES Filed March 24; 1958 INV'Q IIT a R Re MnnLb film Fm,

aw. 7701f:-

United States Pa ELECTRIC SWITCHES Reginald Arthur Firman, Weybridge, England, assignor to Viekers-Armstrongs (Aircraft) Limited, London, England Application March 24, 1958, Serial No. 724,141 Claims priority, application Great Britain April 10, 1957 4 Claims. (Cl. 200-166) The invention has reference to electric switches of the type in which the respective contacts are constituted by two bar-like elements disposed substantially at right angles to each other, one of such contacts being traversed along the face of the other contact to complete a circuit through the same.

Where, in a switch of such type, contact has to be maintained over a certain length of relative movement between the contact elements and then interrupted at a predetermined point, it has hitherto been proposed in certain cases to use as one of the contact elements a spring strip. Where the moving element rotated about a pivot, it was important that the pressure between the elements during contact should be light, in order to minimise the braking effect on the pivotal element and to reduce Wear due to friction. Electrical contact resistance is a function of area of contact, and in view of the inevitable irregularities in the surfaces of the contact elements, the greater the area of contact required, the greater must be the load. This load is disadvantageous by reason of the increased braking efiect and frictional wear which it entails. If however the contact load is reduced to minimise braking effect, the unevenness of the contacting surfaces of the elements will cause arcing as they pass from one high point to another, with eventual increased electrical contact resistance.

When in such a switch a spring strip stationarycontact is employed, the mechanical follow-up at break due to the sudden relief of spring tension tends to reduce the speed of break and thus tends to draw the are caused at the break. Where the moving contact element oscillates at high frequency, the resultant bounce of the spring strip is undesirable. Where the contact pressure is maintained by interference between the elements at the time of assembly, the pressure is a function of the interference, which may vary greatly and would be incapable of being detected by checking the continuity of the circuit.

In a switch of the, specified type according to the present invention the foregoing disadvantages are avoided by an arrangement wherein one of the switch elements, conveniently though not necessarily the stationary element, is sub-divided longitudinally into a plurality of members of convex cross-section which are electrically connected but independently supported at each end in a pre-tensioned condition, with capability of individual resilience, so as severally to make virtual point-to-point contact with a transversely disposed bar element having a convex contact face.

One embodiment of the invention is diagrammatically illustrated in the accompanying drawing, of which Fig. 1 is a side elevation of the switch showing the operative relationship of the moving and stationary elements, whilst Fig. 2 is a front elevation of the stationary contact-element alone.

In the drawings, is a holder which is slotted at 101,

Patented Oct. 6, 1959 101, so that a plural of lengths of metal wire 11 of convex (i.e. circular) cross-section may be assembled and located as shown, the wires being successively slid sideways into the slots and retained in position by a keepplate 102. The end 111 of each wire 11 is bent as shown over a separate member 12, so that when the latter is fixed in position on the holder 10, the parts 111 are pretensioned at upper and lower ends.

The moving contact-element is a bar 13 disposed substantially at right angles to the length of the wire sections 11. It may be adapted for rectilinear movement in relation to the wire sections 11, or, as in the embodiment illustrated, it may be mounted on an arm 14 which pivots about an axis 15 so that the bar 13 is caused to traverse the parts 112 of said wire sections in the direction of the arrow, bearing against each section individually.

Such an arrangement, which provides virtually point-topoint contact between the switch elements, and wherein the individual sections 111 of the stationary switch element 11 are free to flex as the bar 13 moves over any irregularities in their surfaces, gives the maximum pressure between the contacts for any given pre-tension, this pressure assisting in maintaining the contact surfaces in a clean condition. The current flowing through the switch is divided between the several sections 111 throughout the stroke of the bar 13, the lower current per section giving a high contact efficiency, and a small arc at break. The arrangement whereby the sections 111 are pretensioned at each end facilitates regulation of the contact pressure and, together with the fact that the individual sections 11 are of low mass and constrained by the holder 12, tends to avoid bounce at break when the switch is operated at high frequency.

What I claim as my invention and desire to secure by Letters Patent is:

1. A switch of the kind described, in which one of the elements is sub-divided into a plurality of electrically connected individually resilient members each of which is of convex cross-section and is independently supported at its ends, in. a prestressed condition, a bar element having a convex contact face, means for mounting said bar element transversely to the resilient members for relative movement therealong with the convex contact face in virtual point-to-point contact with said resilient members, and means for supporting said resilient members with the ends thereof free for movement.

2. A switch according to claim 1 in which said transversely disposed bar element is pivoted about an axis which is at right angles to the said members.

3. A switch according to claim 1 in which the members of the subdivided element are shaped to provide progressively increased mechanical resistance to the movement across the same of the transversely disposed bar element.

4. The switch according to claim 2 wherein the resilient members are supported with both ends of each member free for movement in the direction toward and away from said bar element.

References Cited in the file of this patent UNITED STATES PATENTS 2,520,258 Pittman et a1 Aug. 29, 1950 FOREIGN PATENTS 33,332 France Apr. 10, 1926 (Addition to French Patent 592,873) 134,748 Germany Oct. 3, 1902 592,873 France May 8, 1925 694,556 Germany Aug. 3, 1940 

